I don’t know for a fact, but it wouldn’t surprise me if ELO made heavy use of an Eventide unit to get that really tight, pitch-perfect harmonization. I don’t object to that, but personally never cared for it. I much prefer the sound groups like the Raspberries or even ABBA would achieve – natural, simple, and gorgeous.
Of course NONE of them come close to the rich, beautiful harmonies that the old groups got, groups like the Moonglows, Platters, Pied Pipers, etc.
I’m not a big fan of harmonizing with oneself. Obviously, if you’re doing your own thang at home on your DAW, it’s better than nothing. But I think it’s often better to employ somebody else with a voice that compliments your own.
The great harmony duo’s were, uh, great because of the interesting ways their voices combined with each other: Everly Bros… John, Paul, and often George… Simon and Garfunkel.
Michael Jackson (by way of Quincy Jones) created some nice harmonies with himself, however, and it sounds like he made pretty heavy use of a Harmonizer. It worked for him, and the music of his era.
Except for Country, I think those days are past us.
I know I haven’t addressed your question… sorry